Heat exchanger

ABSTRACT

Disclosed is a heat exchanger that includes a tubular outer wall and partition walls that partition an inner side of the outer wall into heat medium passage cells and gas passage cells extending in an axial direction of the outer wall. The heat exchanger exchanges heat between a liquid heat medium flowing through the heat medium passage cells and a gas flowing through the gas passage cells. The ratio of the number of the heat medium passage cells to the number of the gas passage cells is 1:3 to 1:6.

TECHNICAL FIELD

The present invention relates to a heat exchanger.

BACKGROUND ART

As shown in FIG. 14, a heat exchanger 40 of Patent Document 1 includesan outer wall 41 and partition walls 44. The outer wall 41 has the formof a rectangular tube. The partition walls 44 partition the inner sideof the outer wall 41 into a plurality of first cells 42 and a pluralityof second cells 43 extending in an axial direction of the outer wall 41.In a cross section orthogonal to the axial direction of the outer wall41, the first cells 42 and the second cells 43 are arranged in lines ina vertical direction. Specifically, from the left side of the plane ofFIG. 14, the first cells 42 are located in the first, third, fifth, andseventh lines, and the second cells 43 are located in the second,fourth, sixth, and eighth lines. In the heat exchanger 40, heat isexchanged between a first fluid flowing through the first cells 42 and asecond fluid flowing through the second cells 43.

The heat exchanger 40 of Patent Document 1 is set so that each secondcell 43 has a cross-sectional flow area that is larger than that of eachfirst cell 42. When heat is exchanged between fluids having differentthermal capacities, the second fluid having a smaller thermal capacityflows through the second cells 43 having a larger cross-sectional flowarea to increase the amount of the second fluid in the heat exchanger40. This matches the thermal capacity of the first fluid as a whole withthe thermal capacity of the second fluid as a whole in the heatexchanger 40 and increases the heat exchange efficiency.

PRIOR ART LITERATURE Patent Literature

Patent Document 1: Japanese Laid-Open Patent Publication No. 2015-140960

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

A heat exchanger such as that shown in FIG. 14 may be used to exchangeheat between a gas, such as exhaust gas, and a liquid heat medium, suchas a coolant. In this case, the heat of the gas is transferred throughthe partition walls of the heat exchanger to the liquid heat medium.However, it is difficult to increase the heat exchange efficiency of theheat exchanger because the heat of the gas transferred to the partitionwalls is limited. Accordingly, one object of the present invention is toprovide a heat exchanger that increases the heat exchange efficiency.

Means for Solving the Problems

A heat exchanger in accordance with the present invention that solvesthe above problem includes a tubular outer wall and partition walls thatpartition an inner side of the outer wall into heat medium passage cellsand gas passage cells extending in an axial direction of the outer wall.The heat exchanger exchanges heat between a liquid heat medium flowingthrough the heat medium passage cells and a gas flowing through the gaspassage cells. The ratio of the number of the heat medium passage cellsto the number of the gas passage cells is 1:3 to 1:6.

With this structure, the number of gas passage cells is three times orgreater than the number of heat medium passage cells thereby increasingthe total cross-sectional flow area of the gas passage cells anddecreasing the velocity of the gas flowing through the gas passagecells. This increases the amount of time of contact between the gas andthe partition walls and also increases the area of contact between thegas and the partition walls. Thus, the heat of the gas is readilytransferred to the partition walls. Also, the number of the gas passagecells are less than or equal to six times of the number of the heatmedium passage cells. This allows the liquid heat medium flowing throughthe heat medium passage cells to completely cool the partition walls.When the partition walls are cooled completely, the heat of the gas willbe quickly transferred. As a result, the heat exchange efficiency of theheat exchanger is increased.

With the heat exchanger in accordance with the present invention, it ispreferred that the outer wall has the form of a rectangular tube thatincludes two opposing first side walls and two opposing second sidewalls. Further, it is preferred that the heat medium passage cells andthe gas passage cells are arranged in heat medium passage cell lines andgas passage cell lines that are parallel to the first side walls in across section orthogonal to the axial direction of the outer wall.Preferably, three to six of the gas passage cell lines are arrangedbetween two adjacent ones of the heat medium passage cell lines in adirection extending along the second side walls. With this structure,the concentrated arrangement of the heat medium passage cells and thearrangement of most of the heat medium passage cells in a certain rangeof the gas passage cells facilitate the partition walls to be completelycooled and reduces pressure loss.

With the heat exchanger in accordance with the present invention, it ispreferred that the outer wall has one side including an inlet and anoutlet for a heat medium that are connected with the heat medium passagecells. With this structure, the arrangement of the inlet and the outletfor the heat medium in one side of the heat exchanger decreases thetotal volume when connecting, for example, pipes through which the heatmedium flows.

With the heat exchanger of the present invention, it is preferred thatthe heat medium passage cells each have the same cross-sectional shapeand the gas passage cells each have the same cross-sectional shape in across section orthogonal to the axial direction of the outer wall. Thisstructure eliminates differences in the heat exchange efficiency betweenthe gas passage cells and differences in the heat exchange efficiencybetween the heat medium passage cells, which would have otherwise beencaused by different cross-sectional shapes. This also reduces pressureloss in the gas passage cells.

With the heat exchanger of the present invention, it is preferred thateach of the heat medium passage cells has a cross-sectional shape thatis larger in size than that of each of the gas passage cells in a crosssection orthogonal to the axial direction of the outer wall. The heatmedium flowing through the heat medium passage cells is a liquid. Thus,the heat medium has a larger passage resistance than the gas whenflowing through the cells. This structure facilitates the flow of theheat medium having a higher flow resistance.

With the heat exchanger of the present invention, it is preferred thatthe partition walls include silicon carbide as a main component. Thesilicon carbide has a relatively high thermal conductivity among ceramicmaterials. Thus, this structure increases the thermal conductivity ofthe partition walls and increases the heat exchange efficiency of theheat exchanger.

Effect of the Invention

The present invention succeeds in increasing heat exchange efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a heat exchanger.

FIG. 2 is a cross-sectional view taken along line 2-2 in FIG. 1.

FIG. 3 is a cross-sectional view taken along line 3-3 in FIG. 2.

FIG. 4 is a cross-sectional view taken along line 4-4 in FIG. 2.

FIG. 5 is a diagram illustrating a molding step.

FIG. 6 is a diagram illustrating a processing step (a diagramillustrating a state in which a processing jig for a first process isstuck in a molded body).

FIG. 7 is a diagram illustrating the processing step (a diagramillustrating a state in which the processing jig for the first processis stuck in and then pulled out of the molded body).

FIG. 8 is a diagram illustrating the processing step (a diagramillustrating a second process).

FIG. 9 is a diagram illustrating a degreasing step.

FIG. 10 is a diagram illustrating an impregnation step.

FIG. 11 is a front view of a heat exchanger of a modified example.

FIG. 12 is a schematic diagram showing a dimension measurement point ina simulation.

FIG. 13 is a temperature distribution chart obtained from thesimulation.

FIG. 14 is a cross-sectional view of a prior art heat exchanger.

MODES FOR CARRYING OUT THE INVENTION

One embodiment of a heat exchanger will now be described.

As shown in FIGS. 1 and 2, a heat exchanger 10 of the present embodimentincludes an outer wall 11 and partition walls 12. The outer wall 11 hasthe form of a rectangular tube. The partition walls 12 partition theinner side of the outer wall 11 into a plurality of heat medium passagecells 13 a and a plurality of gas passage cells 13 b extending in anaxial direction of the outer wall 11. The outer wall 11, which has theform of a rectangular tube, includes two opposing vertical side walls 11a (first side walls) and two opposing lateral side walls 11 b (secondside walls). The outer wall 11 is configured so that its cross sectionorthogonal to the axial direction is rectangular and laterallyelongated.

As shown in FIG. 2, in a cross section orthogonal to the axial directionof the outer wall 11, the partition walls 12 form a grid-like cellstructure and include partition walls 12 parallel to the vertical sidewalls 11 a and partition walls 12 parallel to the lateral side walls 11b. The cell structure of the partition walls 12 is not particularlylimited. For example, the cell structure may be configured so that thepartition walls 12 have a thickness of 0.1 to 0.5 mm and a cell densityof 15 to 93 cells per 1 cm² in a cross section orthogonal to the axialdirection of the outer wall 11.

As shown in FIG. 3, the heat medium passage cells 13 a, through which aheat medium flows, each include two ends that are sealed by a sealedportion 22. As shown in FIG. 4, each gas passage cell 13 b, throughwhich a gas subject to processing flows, includes two open ends. Theheat medium is not particularly limited and a known liquid heat mediummay be used. Examples of known heat medium include a coolant (long lifecoolant (LLC)) and an organic solvent, such as ethylene glycol. The gassubject to processing may be, for example, exhaust gas of an internalcombustion engine.

As shown in FIG. 2, in a cross section orthogonal to the axial directionof the outer wall 11, each heat medium passage cell 13 a has the samecross-sectional shape as the gas passage cells 13 b.

As shown in FIG. 2, the heat exchanger 10 includes a plurality of heatmedium passage cell lines 14 a and a plurality of gas passage cell lines14 b. The heat medium passage cell lines 14 a include only the heatmedium passage cells 13 a arranged parallel to the vertical side walls11 a of the outer wall 11, and the gas passage cell lines 14 b includeonly the gas passage cells 13 b arranged parallel to the vertical sidewalls 11 a.

The heat exchanger 10 is set so that the ratio of the number of the heatmedium passage cells 13 a to the number of the gas passage cells 13 b isin a certain range. The ratio (heat medium passage cells 13 a:gaspassage cells 13 b) is 1:3 to 1:6, and preferably, 1:4 to 1:5.

In the present embodiment, the ratio is adjusted by the arrangement ofthe heat medium passage cell lines 14 a and the gas passage cell lines14 b. Specifically, in a direction extending along the lateral sidewalls 11 b of the outer wall 11, a plurality of gas passage cell lines14 b are arranged between two adjacent heat medium passage cell lines 14a. This arrangement is repeated in the direction of the lateral sidewalls 11 b of the outer wall 11 to form an arrangement pattern. When thenumber of the gas passage cell lines 14 b arranged between two adjacentheat medium passage cell lines 14 a is three to six, the ratio is 1:3 to1:6. Preferably, the number of the gas passage cell lines 14 b arrangedbetween two adjacent heat medium passage cell lines 14 a is four tofive.

As shown in FIGS. 1 and 3, in the heat exchanger 10, the heat mediumpassage cell lines 14 a each include a connection portion 15 extendingin the vertical direction. The connection portion 15 extends through thepartition walls 12 between adjacent heat medium passage cells 13 a inthe vertical direction and connects the cells of heat medium passagecell lines 14 a. The connection portion 15 has an end at one side in thevertical direction (upper side in FIG. 3) that opens in the outer walls11 (lateral side wall 11 b) and an end at the other side in the verticaldirection (lower side in FIG. 3) reaching the heat medium passage cell13 a that is the farthest from the opening of the connection portion 15.In other words, each connection portion 15 opens in one side of theouter wall 11 and extends to the heat medium passage cell 13 a that isthe farthest from the opening of the connection portion 15. Theconnection portion 15 of the heat exchanger 10 includes a firstconnection portion 15 a and a second connection portion 15 b. The firstconnection portion 15 a is arranged closer to a first end 10 a, which islocated at one side in the axial direction of the heat exchanger 10, andthe second connection portion 15 b is arranged closer to a second end 10b, which is located at the other side in the axial direction of the heatexchanger 10.

As shown in FIG. 3, a heat medium flow passage 16 is formed inside theheat exchanger 10 by the heat medium passage cells 13 a, the firstconnection portion 15 a, and the second connection portion 15 b. Theopening of the first connection portion 15 a and the opening of thesecond connection portion 15 b in the outer wall 11 of the heatexchanger function as an inlet or an outlet of the heat medium flowpassage 16. Further, as shown in FIG. 4, a gas flow passage 17 is formedinside the heat exchanger 10 by each gas passage cell 13 b, with itsaxial ends 10 a and 10 b functioning as an inlet or an outlet of the gasflow passage 17. The heat exchanger 10 exchanges heat through thepartition walls 12 between the heat medium flowing through the heatmedium flow passages 16 and the gas flowing through the gas flowpassages 17.

The material of the outer wall 11, which has the form of a rectangulartube, and the partition walls 12 of the heat exchanger 10 is notparticularly limited. The material of a known heat exchanger may beused. The material is, for example, a carbide, such as silicon carbide,tantalum carbide, and tungsten carbide, or a nitride, such as siliconnitride and boron nitride. Among these substances, a material includingsilicon carbide as a main component is preferred since it has a higherthermal conductivity than other ceramic materials and increases the heatexchange efficiency. Here, “main component” refers to a component thatis greater than or equal to 50% by mass. An example of a materialincluding silicon carbide as a main component is a material includingsilicon carbide particles and metal silicon.

A method for manufacturing the heat exchanger of the present embodimentwill now be described with reference to FIGS. 5 to 10. The heatexchanger is manufactured by sequentially performing a molding step, aprocessing step, a degreasing step, and an impregnation step asdescribed below.

Molding Step

As a raw material for molding the heat exchanger, silicon carbideparticles, an organic binder, and a dispersion medium are mixed toprepare a clay-like mixture. A molded body 20 shown in FIG. 5 is moldedfrom the clay-like mixture. The molded body 20 includes the outer wall11, which has the form of a rectangular tube, and the partition walls12, which partition the inner side of the outer wall 11 into a pluralityof cells 13 extending in the axial direction of the outer wall 11. Thecells 13 in the molded body 20 each have two open ends. The molded body20 can be molded, for example, by extrusion molding. A drying process isperformed on the obtained molded body 20 to dry the molded body 20.

Processing Step

In the processing step, a first process and a second process areperformed. The first process is performed to form first connectionportions and second connection portions in the molded body. The secondprocess is performed to seal the two ends in some of the cells of themolded body.

As shown in FIG. 6, in the first process, for example, the firstconnection portions 15 a and the second connection portions 15 b areformed by a heated processing tool 21 that contacts the molded body andremoves parts of the outer wall 11 and the partition walls 12 of themolded body 20.

Specifically, as shown in FIG. 6, a blade having a contour thatcorresponds to the first connection portion 15 a and the secondconnection portion 15 b is prepared as the processing tool 21. The bladeis formed from a heat resistant metal (e.g., stainless steel) and has athickness that is set so as not to exceed the width of the heat mediumpassage cell 13 a. Subsequently, the blade is heated to a temperature atwhich the organic binder included in the molded body 20 is burned andremoved. For example, when the organic binder is methyl cellulose, theblade is heated to 400° C. or higher.

As shown in FIG. 7, the heated blade is stuck into the molded body 20from an outer side and then pulled out to form the first connectionportions 15 a and the second connection portions 15 b. In this case,when the heated blade contacts the molded body 20, the organic binderincluded in the molded body 20 is burned and removed at the contactportion. Thus, the insertion resistance of the molded body 20 againstthe blade is extremely small. This limits deformation and breakagearound the portion where the blade is stuck. Further, the burned andremoved organic binder reduces the amount of processing waste.

As shown in FIG. 8, in the second process, among the cells 13 of themolded body 20, two ends of each cell 13 defining one heat mediumpassage cell 13 a are sealed with the clay-like mixture used in themolding step. This forms the sealed portions 22 that seal the two endsof the cell 13. Then, a drying process is performed on the molded body20 to dry the sealed portions 22.

A processed molded body is obtained by performing the processing stepincluding the first process and the second process. The order in whichthe first process and the second process are performed is notparticularly limited. The first process may be performed after thesecond process.

Degreasing Step

In the degreasing step, the processed molded body is heated to burn andremove the organic binder included in the processed molded body. Thisremoves the organic binder from the processed molded body and obtains adegreased body. As shown in FIG. 9, a degreased body 30, in which theorganic binder is removed from the processed molded body in thedegreasing step, has a frame portion arranged in a state in whichsilicon carbide particles are in contact with one another.

Impregnating Step

In the impregnation step, the inside of each wall forming the degreasedbody is impregnated with metal silicon. In the impregnation step, thedegreased body is heated in a state contacting a cluster of metalsilicon to a melting point of the metal silicon or higher (for example,1450° C. or higher). As shown in FIG. 10, molten metal silicon entersthe voids between particles, which form the frame portion of thedegreased body, through capillary action and impregnates the voids.

The heating process in the impregnation step may be performedsuccessively with the heating process of the degreasing step. Forexample, in a state contacting a cluster of metal silicon, the processedmolded body may be heated at a temperature lower than the melting pointof metal silicon to remove the organic binder and obtain the degreasedbody. Then, the heating temperature may be raised to the melting pointof the metal silicon or higher to impregnate the degreased body with themolten metal silicon.

The heat exchanger is obtained by performing the impregnation step.

In the present embodiment, special temperature management is performedin the steps from the degreasing step. Specifically, the steps from thedegreasing step are performed at a lower temperature than a sinteringtemperature of the silicon carbide included in the mixture used in themolding step so that the processed molded body and the degreased bodyare not exposed to a temperature higher than or equal to the sinteringtemperature. Therefore, in the degreasing step, heating is performed ata temperature that is higher than or equal to a temperature that burnsand removes the organic binder and lower than the sintering temperature.In the same manner, in the impregnation step, heating is performed at atemperature higher than or equal to the melting point of metal siliconand lower than the sintering temperature.

The operation and advantages of the present embodiment will now bedescribed.

(1) The ratio of the number of the heat medium passage cells to the gaspassage cells of the heat exchanger is 1:3 to 1:6. The number of the gaspassage cells is three times or greater than the number of the heatmedium passage cells. Thus, a total cross-sectional flow area of the gaspassage cells is increased, and the velocity of the gas flowing throughthe gas passage cells is decreased. This increases the amount of time ofcontact between the gas and the partition walls and the area of contactbetween the gas and the partition walls thereby allowing heat to bereadily transferred from the gas to the partition walls. Also, thenumber of the gas passage cells is less than or equal to six times ofthe number of the heat medium passage cells. This allows the liquid heatmedium flowing through the heat medium passage cells to completely coolthe partition walls. When the partition walls are completely cooled, theheat of the gas will be quickly transferred. As a result, the heatexchange efficiency of the heat exchanger is increased.

(2) Three to six gas passage cell lines are arranged between twoadjacent heat medium passage cell lines. The concentrated arrangement ofthe heat medium passage cells and the arrangement of most of the heatmedium passage cells in a certain range of the gas passage cellsfacilitate the partition walls to be completely cooled. Further,pressure loss is reduced.

(3) The inlets and the outlets for the heat medium, which are connectedwith the heat medium passage cells, are located in the same side of theouter wall. The arrangement of the inlets and the outlets of the heatmedium on one side of the heat exchanger allows the total volume to bedecreased when connecting, for example. pipes through which the heatmedium flows.

(4) In a cross section orthogonal to the axial direction of the outerwall, the heat medium passage cells each have the same cross-sectionalshape, and the gas passage cells each have the same cross-sectionalshape. This eliminates differences in the heat exchange efficiencybetween the gas passage cells and differences in the heat exchangeefficiency between the heat medium passage cells that would result fromdifferent cross-sectional shapes.

(5) The partition walls include silicon carbide as a main component.Among ceramic materials, silicon carbide has a relatively high thermalconductivity. Thus, the partition walls, which include silicon carbideas a main component, have high thermal conductivity. This increases theheat exchange efficiency of the heat exchanger.

(6) The heat exchanger of the present embodiment is manufactured byperforming temperature management as described above. The frame portionis formed in a state in which the silicon carbide particles are incontact with one another, and the shape of the frame portion is heldwith the voids filled with the silicon carbide. In other words, thesilicon carbide particles do not include connected portions (necks),which result from sintering. This prevents cracking of necks between thesilicon carbide particles even when internal temperature differencescause distortion in the partition walls during use of the heatexchanger. This further prevents cracks from spreading through necks.

The present embodiment may be modified as described below. Also, theconfiguration of the above embodiment and following modifications may becombined.

-   -   In the present embodiment, the cells are arranged in the        vertical direction of the outer wall, which has the form of a        rectangular tube. However, the cells do not have to be arranged        in the vertical direction. The heat exchanger may be used        sideways and the cells may be arranged in a lateral direction.    -   The heat medium passage cell lines are not limited to a        configuration that only includes the heat medium passage cells.        The heat medium passage cell lines may be configured so that 80%        or more of the cells are the heat medium passage cells. Further,        the gas passage cell lines are not limited to a configuration        that only includes the gas passage cells. The heat gas passage        cell lines may be configured so that 80% or more of the cells        are the gas passage cells. That is, 20% or less of the heat        medium passage cell lines may be the gas passage cells. Further,        20% or less of the heat medium passage cell lines may be the        heat medium passage cells.    -   The outer wall does not need to have the form of a rectangular        tube. The outer wall may have the form of a round tube or a tube        having an elliptic cross section. Also, the partition walls do        not have to be grid-like in which the partition walls intersect        each other at approximately 90°. The partition walls may be        configured so that the cells have cross sections other than        rectangular cross sections, such as rhombic or polygonal cross        sections. For example, the partition walls may be configured to        have hexagonal cross sections.

When the outer wall does not form a rectangular tube or when thepartition walls are not grid-like and the partition walls do notintersect each other at approximately 90°, the outer wall may form cellswith the partition walls that are shaped differently from the othercells. For example, in a configuration in which the partition walls formcells having hexagonal cross sections, the outer wall may form cellswith the partition walls that have pentagonal or rectangular crosssections.

-   -   The heat medium passage cells may have different cross-sectional        shapes. The gas passage cells may have different cross-sectional        shapes.    -   In the present embodiment, the outer wall and the partition        walls are formed of a material including silicon carbide as a        main component. Instead, only the partition walls may be formed        of a material including silicon carbide as a main component.        Alternatively, the outer wall and the partition walls may be        formed of a material other than one including silicon carbide as        a main component.    -   The cross-sectional shapes of the heat medium passage cells and        the gas passage cells may differ in size in a cross section        orthogonal to the axial direction of the outer wall. For        example, as shown in FIG. 11, the heat medium passage cell 13 a        may be configured to have a larger widthwise dimension than the        gas passage cells 13 b so that the cross-sectional shape of each        heat medium passage cell is increased in size. The liquid heat        medium flowing through the heat medium passage cells has a        greater passage resistance than a gas when flowing through the        cells. Thus, when the heat medium passage cells each have a        larger cross-sectional shape than the gas passage cells, the        heat medium flows more smoothly. For example, in the        configuration shown in FIG. 11, the widthwise dimension of the        heat medium passage cell may be 1.0 to 5.0 mm, and the widthwise        dimension of the gas passage cell may be 0.9 to 2.5 mm.        Alternatively, the heat medium passage cells may each have a        smaller widthwise dimension than the gas passage cells.    -   In a configuration in which three to six gas passage cell lines        are arranged between two adjacent heat medium passage cell        lines, the number of the gas passage cell lines, which is three        to six, does not have to be fixed. That is, the number of the        gas passage cell lines may vary from three to six.    -   As long as the ratio of the heat medium passage cells to the gas        passage cells is 1:3 to 1:6, the arrangement of the heat medium        passage cells and the gas passage cells is not limited to the        configuration in which three to six gas passage cell lines are        arranged between two adjacent heat medium passage cell lines.        The ratio of the number of the heat medium passage cells to the        gas passage cells being 1:3 to 1:6 means that, for example, in        any group of four vertical cells×seven lateral cells, there is        four to seven heat medium passage cells.

EXAMPLES

Specific examples of the above described embodiment will now bedescribed.

Example 1

First, a mixture having the composition described below was prepared.

Particles of silicon carbide with average particle size of 15 μm (largeparticles): 52.5 parts by mass

Particles of silicon carbide with average particle size of 0.5 μm (smallparticles): 23.6 parts by mass

Methyl cellulose (organic binder): 5.4 parts by mass

Glycerol (lubricant): 1.1 parts by mass

Polyoxyalkylene compound (plasticizer): 3.2 parts by mass

Water (dispersion medium): 11.5 parts by mass

With this mixture, a molded body was molded to have a honeycombstructure in which the height was 50 mm, the width was 100 mm, thelength was 100 mm, the thickness of the outer wall was 0.3 mm, thethickness of the partition walls was 0.25 mm, and the cell width was 1.2mm.

Next, a plate-like jig heated to 400° C. was stuck into the outer wallof the molded body to form the first connection portions and the secondconnection portions. Then, predetermined cells were sealed with aclay-like mixture having the same composition as the above-describedmixture to form the processed molded body in which four gas passage celllines were arranged between two adjacent heat medium passage cell lines.In other words, in the processed molded body, the ratio of the number ofthe heat medium passage cells to the number of the gas passage cells was1:4. Subsequently, the processed molded body was heated at 450° C. forfive hours to remove the organic binder and obtain the degreased body.Then, the degreased body was heated at 1550° C. for seven hours in avacuum in a state in which a 20 gram-metal silicon plate is placed onthe degreased body to impregnate the degreased body with metal siliconand obtain the heat exchanger of example 1.

Evaluation Tests

The heat exchanger of example 1 was evaluated for temperaturedistribution in the heat medium passage cells and the gas passage cellsby a simulation. Further, heat exchangers of examples 2 to 4 wereevaluated for temperature distribution under the same condition asexample 1 except in that the number of the gas passage cell linesbetween two adjacent heat medium passage cell lines was set to three,five, and six, that is, the ratio of the numbers of the heat mediumpassage cells to the gas passage cells was set to 1:3, 1:5, and 1:6.Also, heat exchangers of comparative example 1 and 2 were evaluated fortemperature distribution under the same condition as example 1 except inthat the number of the gas passage cell lines between two adjacent heatmedium passage cell lines was set to two and eight, that is, the ratioof the numbers of the heat medium passage cells to the gas passage cellswas set to 1:2 and 1:8.

Simulation Condition

A simulation condition is described as below. FIG. 12 shows wheremeasurements were taken with regard to the dimensions of a cell.

-   -   Cell height T: 1.2 mm, cell width H: 1.2 mm, length of heat        medium passage cell: 100 mm, length of gas passage cell: 100 mm    -   Partition wall thickness W: 0.25 mm, thermal conductivity of        partition wall: 190 W/m*K    -   Temperature of heat medium: 40° C., flow rate of heat medium: 10        L/min    -   Temperature of gas: 400° C., flow rate of gas: 10 g/sec    -   Name of simulation software: Fluent (registered trademark,        manufactured by ANSYS)

FIG. 13 shows the results of the simulation.

The left column in FIG. 13 shows the temperature distribution at acentral portion in the axial direction of the heat exchanger (10 mm fromaxial end), and the right column in FIG. 13 shows the temperaturedistribution at an outlet side of the heat exchanger (90 mm from axialend). The temperature distribution in the cells is shown in differentcolors.

First, the temperature distribution of example 1 will be described.Halves of the heat medium passage cells (½ of each cell) were arrangedat the left side, and two lines of the gas passage cells were located atthe right side of the heat medium passage cells to set the ratio of thecells to 1:4. Then, the heat medium and the gas were distributed under apredetermined condition to measure the temperature distribution in theheat medium passage cells, the partition walls, and the gas passagecells.

As shown in FIG. 13, in examples 1 to 4, the heat medium passage cellsand the partition walls were each less than or equal to 50° C. Thisindicates that the partition walls were completely cooled. At thecentral portion in the axial direction of the heat exchanger, themaximum temperature in the gas passage cells was lower than or equal to120° C. At the outlet side of the heat exchanger, the maximumtemperature in the gas passage cells was lower than or equal to 58° C.In particular, in examples 1 and 3, the region in which the temperaturewas close to 58° C. was limited at the outlet side of the heatexchanger. Thus, it was confirmed that the gas in the gas passage cellswas cooled in a preferred manner and the heat exchange efficiency washigh.

In contrast, in comparative examples 1 and 2, at the central portion inthe axial direction of the heat exchanger, the maximum temperature inthe gas passage cells was higher than or equal to 120° C. At the outletside of the heat exchanger, the maximum temperature in the gas passagecells was higher than or equal to 58° C. Also, in comparative example 2,a region in which the temperature of the partition walls was 50° C. orhigher was present at the central portion in the axial direction of theheat exchanger and thus the partition walls were not completely cooled.Thus, it was confirmed that the heat exchange efficiency was low.

DESCRIPTION OF THE REFERENCE NUMERALS

10) heat exchanger, 11) outer wall, 12) partition wall, 13 a) heatmedium passage cell, 13 b) gas passage cell.

1. A heat exchanger, comprising: a tubular outer wall; and partitionwalls that partition an inner side of the outer wall into heat mediumpassage cells and gas passage cells extending in an axial direction ofthe outer wall, wherein the heat exchanger exchanges heat between aliquid heat medium flowing through the heat medium passage cells and agas flowing through the gas passage cells, and the ratio of the numberof the heat medium passage cells to the number of the gas passage cellsis 1:3 to 1:6.
 2. The heat exchanger according to claim 1, wherein theouter wall has the form of a rectangular tube that includes two opposingfirst side walls and two opposing second side walls, the heat mediumpassage cells and the gas passage cells are arranged in heat mediumpassage cell lines and gas passage cell lines that are parallel to thefirst side walls in a cross section orthogonal to the axial direction ofthe outer wall, and three to six of the gas passage cell lines arearranged between two adjacent ones of the heat medium passage cell linesin a direction extending along the second side walls.
 3. The heatexchanger according to claim 1, wherein the outer wall has one sideincluding an inlet and an outlet for a heat medium that are connectedwith the heat medium passage cells.
 4. The heat exchanger according toclaim 1, wherein the heat medium passage cells each have the samecross-sectional shape and the gas passage cells each have the samecross-sectional shape in a cross section orthogonal to the axialdirection of the outer wall.
 5. The heat exchanger according to claim 1,wherein each of the heat medium passage cells has a cross-sectionalshape that is larger in size than that of each of the gas passage cellsin a cross section orthogonal to the axial direction of the outer wall.6. The heat exchanger according to claim 1, wherein the partition wallsinclude silicon carbide as a main component.